1. Field of the Invention
The present invention relates to a charging device and an image forming apparatus provided with the charging device, and more particularly to a charging device for charging an image bearing member and an image forming apparatus provided with the charging device.
2. Description of Related Art
An example of conventional charging devices is a charging device as disclosed by Japanese Patent Laid-Open Publication No. 11-258891 (Reference 1). FIG. 13 shows a part of the charging device 500 disclosed by Reference 1.
In FIG. 13, a charging wire 501, grinding pads 502 and 504, cleaning pads 506 and 508 are shown. The charging wire 501 is one wire, and a high voltage is applied to the charging wire 501 from a high-voltage source. Thereby, a discharge from the charging wire 501 occurs. As the discharge occurs again and again, silicon oxide and other substances adhere to the charging wire 501, and corona products, which are called as needles, are formed on the charging wire 501. Due to the corona products, the discharge from the charging wire 501 becomes uneven, thereby causing a fault in charging. This is a cause of image noise.
In order to avoid this trouble, the grinding pads 502 and 504 are moved in a direction shown by arrow “A” while nipping the charging wire 501 in-between. Thereby, the corona products adhering to the charging wire 501 is ground by the grinding pads 502 and 504. Following the grinding pads 502 and 504, the cleaning pads 506 and 508 are moved in the direction “A” while nipping the charging wire 501 in-between. Thereby, abrasive grains that peeled off from the grinding pads 502 and 504 and the corona products are wiped out. Thus, in the charging device 500, the charging wire 501 is cleaned by two processes, namely, grinding and wiping.
In recent years, charging devices of a type having a sheet electrode with aligned triangular pins are replacing charging devices 500 of the above-described type having a charging wire. The type of charging devices having a sheet electrode has the advantage over the charging device disclosed by Reference 1 of generating less ozone. However, the type of charging devices having a sheet electrode has the same problem as the charging device disclosed by Reference 1 in that corona products are generated. Therefore, also in this type of charging devices, it is necessary to clean the sheet electrode regularly.
The type of charging devices having a sheet electrode has also a problem that the pins are fragile. FIGS. 14a and 14b show wiping of a sheet electrode 600.
More specifically, an exemplary way of cleaning the sheet electrode 600 is touching grinding pads and cleaning pads as disclosed by Reference 1 to main surfaces of the sheet electrode 600. As the grinding pads, for example, sheets 601 with abrasive grains scattered thereon are used. As the cleaning pads, for example, two pieces of pile fabric 602 with brush fibers standing thereon as shown in FIGS. 14a and 14b are used. As shown by FIG. 14a, by moving the sheets 601 and the pieces of pile fabric 602 in a direction shown by arrow “B”, it is possible to grind and wipe off corona products from the sheet electrode 600.
In the charging device having the sheet electrode 600, however, when the sheets 601 and the pieces of pile fabric 602 are moved in the direction “B” and thereafter moved in a direction “C” opposite to the direction “B”, the fibers of the pile fabric 602 may twist around the pins of the sheet electrode 600. As shown by FIG. 14a, while the sheets 601 and the pieces of pile fabric 602 are moving in the direction “B”, the fibers of the pile fabric 602 are pulled by a frictional force with the sheet electrode 600 and trail down slanting to the direction “C”, which is the opposite direction to the direction “B”. Thereafter, when the pieces of pile fabric 602 are moved in the direction “C” shown by FIG. 14b, the fibers of the pile fabric 602 are pulled in the direction “B” and are turning around from the direction “C” to the direction “B”. In this moment, the fibers of the pile fabric 602 may twist around the pins of the sheet electrode 600, thereby possibly causing bends of the pins of the sheet electrode 600. Then, bends of the tips of the pins of the sheet electrode 600 will cause a charging fault, thereby resulting in degradation of the picture quality.